Conventional hydraulic tensioners equipped with an oil reservoir and used, for example, for the transmission of a power between a crankshaft and camshafts of an engine include, for example as shown in cross section in FIG. 2, a tensioner body 20 having a cylindrical chamber 21 in which a plunger 22 is slidably fitted, and a shoe 24 fixed to a projecting end of the plunger 22 for sliding contact with a chain 23. The plunger 22 has an internal hollow space forming, jointly with the cylindrical chamber 21, a high pressure chamber 25. A spring 26 is disposed in the hollow space of the plunger 22 and urges the plunger 22 in a direction projecting away from the tensioner body 20.
The tensioner body 20 includes a reservoir portion 27 formed integrally with and projecting laterally from the tensioner body 20. The reservoir portion 27 holds an oil supplied from an engine side and communicates via an oil passage 28 with the inlet side of a check valve 29, the outlet side of the check valve 29 communicating with the high pressure chamber 25.
The conventional hydraulic tensioner of the foregoing construction holds a chain 23 downwardly under tension as the shoe 24 normally urges the chain 23 by the force of the spring 26. When the plunger moves downwardly, the oil in the reservoir 27 flows from the oil passage 28 into the high pressure chamber 25 via the check valve 29 and fills up the high pressure chamber 25.
When an impact force is applied by the chain 23 to the shoe 24, the plunger 22 is forced into the cylindrical chamber 21, whereupon the check valve 29 is closed due to a pressure build-up in the high pressure chamber 25. Consequently, the oil in the high pressure chamber 25 is expelled to the outside of the tensioner body through a clearance between the outside surface of the plunger 22 and the inside surface of the cylindrical chamber 21 during which time the oil forcibly makes a clearance between the outside surface of the plunger 22 and an O-ring 31 fitted in an annular groove 30 formed in the inside surface of the cylindrical chamber 21. With this restricted flow of the oil, the impact force is dampened or otherwise absorbed.
Due to the oil reservoir portion 27 projecting laterally from the tensioner body 20, the aforementioned conventional tensioner device equipped with an oil reservoir is not compact and hence is unsuitable for an application as a chain tensioner device operatively interlocking engine camshafts because in this application, a large space is not available for installation of the tensioner device.
Furthermore, due to the structure employed to allow the oil to escape from the high pressure chamber 25 to the outside of the tensioner body 20 through the clearance between the outside surface of the plunger 22 and the inside surface of the cylindrical chamber 21 in order to absorb the impact force applied to the shoe 24, the O-ring 31 must be provided between the outside surface of the plunger 22 and the inside surface of the cylinder 21 to restrict, and hence offer a resistance to, the flow of the oil. The tensioner body 20 further needs a reservoir portion formed therein. Due to these structural requirements, the manufacturing cost of the conventional tensioner device is increased.